Refrigeration system with multi-stage throttling

ABSTRACT

A REFRIGERATING SYSTEM PROVIDED WITH MULTI-STAGE THROTTLING AND WITH A POSITIVE DISPLACEMENT COMPRESSOR OF THE ROTARY TYPE, THE CASING OF THE COMPRESSOR BEING PROVIDED BETWEEN ITS LOW PRESSURE AND HIGH PRESSURE PORTS WITH ONE OR MORE ADMISSION PORTS FOR INTERMEDIATE PRESSURE GAS FROM LIQUID SEPARATORS LOCATED BETWEEN THROTTLING POINTS. THE GAS FORMED DURING THROTTLING IS SUPPLIED THROUGH THESE ADMISSION PORTS TO THE WORKING COMPARTMENT OF THE COMPRESSOR. THE OPENING AND CLOSING OF THE ADMISSION PORTS IS ACHIEVED BY THE ACTION OF THE COMPRESSOR WHICH HAS ITS ROTOR LOBES OPERATIVE AS VALVES FOR THE ADMISSION PORTS.

March 9, 1971 BRANDlN ET AL REFRIGERATION SYSTEM WITH MULTI-STAGETHROTTLING Filed April 28, 1969 Fig.

3,568,466 REFRIGERATION SYSTEM WITH MULTI-STAGE THROTTLING Tore Brandinand Knut Anders Lennart Lundberg, Norrkoping, Sweden, assignors to StalRefrigeration Aktiebolag, Norrkoping, Sweden Filed Apr. 28, 1969, Ser.No. 819,685 Claims priority, application Sweden, May 6, 1968, 6,054/ 68Int. Cl. F251) 1/10 US. Cl. 62-510 2 Claims ABSTRACT OF THE DISCLOSURE Arefrigerating system provided with multi-stage throtfling and with apositive displacement compressor of the rotary type, the casing of thecompressor being provided between its low pressure and high pressureports with one or more admission ports for intermediate pressure gasfrom liquid separators located between throttling points. The gas formedduring throttling is supplied through these admission ports to theworking compartment of the compressor. The opening and closing of theadmission ports is achieved by the action of the compressor which hasits rotor lobes operative as valves for the admission ports.

In refrigerating systems multi-stage throttling is used in conjunctionwith multi-stage compression and with or without intercooling. Theadvantage of this arrangement is that, for a given swept volume, agreater refrigerating effect is obtained, since a larger enthalpydifference is obtained on the low pressure side. Multi-stage compressionprovides an even lower pressure rise per stage which gives even highervolumetric and total efliciencies. It is usual to employ more than onecompressor or one compressor with more than one working compartment,this is, high pressure and low pressure cylinders in piston compressorsor several wheels operating at different pressure levels in centrifugalcompressors.

The present invention relates to a refrigeration system provided withmulti-stage throttling and with a positive displacement compressor ofthe rotary type and is principally characterized by the fact that thereis provided between the low pressure and high pressure ports in thecompressor, one or several admission ports in the casing of thecompressor, for the admission of intermediate pressure gas from liquidseparators located between the throttling points. The gas formed duringthrottling is supplied through these admission ports to the workingcompartment of the compressor. The opening and closing of the admissionports is achieved by the compressor and in a screw compressor this iscarried out by the rotor lobes. The ports are located in the wall of theworking compartment to obtain the necessary intermediate pressure.

The intermediate pressure of the refrigeration system is determined bythe mean pressure in that part of the working compartment in which theport is located.

Reference is to be had to the accompanying drawing wherein anillustrative embodiment of the invention is disclosed and in which FIG.1 shows the diagrammatic arrangement of a refrigeration system inaccordance with the present invention and FIG. 2 is a longitudinalsectional view through a screw compressor in which the improvements areembodied.

States Patent Ofice Patented Mar. 9, 1971 The compressor is designatedat 1. The gas compressed by the compressor is discharged through a pipe2 to a condenser 3 from which the refrigerant liquid flows through pipe4 and through a throttling device 5 to a liquid separator 6. From theseparator 6 the refrigerant liquid at intermediate pressure flowsthrough another throttling device 8 to an evaporator 9 from which thegas is drawn back into the compressor.

The gas formed during throttling through the throttling device 5 isdrawn through a pipe 10, provided with a control valve 11, to thecompressor through one of several ports 12 in the wall of the compressorcasing. As illustrated on the screw compressor in FIG. 2, the ports 12consist of several small holes located along a spiral line which has thesame pitch angle as the rotor lobes 16 and grooves between the same.This arrangement decreases the amount of leakage across the periphery ofthe rotor lobes from one working compartment which is at a higherpressure, to the succeeding compartment which is at a lower pressure. Inaddition, the positions at which the ports open and close are morereadily defined.

The port 12 for the intermediate pressure gas is connected to adistribution chamber 13 integrally formed on the compressor casing.

Compared with a refrigeration system with single stage throttling, theadvantage of a system made in accordance with the present invention isthat for a given compressor size, the refrigerating effect increasesroughly proportionately with the enthalpy difference. In addition, thespecific power consumption of the compressor is improved since the powerconsumption due to the altered shape of the PV diagram after fillingdoes not increase by the same amount as the enthalpy difference.

The port or ports 12 should preferably be located at a point where gasis supplied to the low pressure gas when the volume of the latter hasdecreased by 30% or more.

The low pressure port is designated at 14 and the high pressure port at15.

What is claimed is:

1. A refrigeration system with multi-stage throttling and with apositive displacement compressor of the rotary type, the compressorhaving a casing provided with high pressure and low pressure ports, saidcasing having at least one admission port, a liquid separator providingintermediate pressure gas to the compressor through the admission portin its casing, the liquid separator being located between throttlingdevices, the compressor being of the screw type and the admission portconsisting of several holes disposed along a spiral line having the samepitch angle as lobes and grooves of a rotor of the compressor.

2. A refrigeration system according to claim 1, wherein the admissionports in the casing for the gas of intermediate pressure, are connectedto a collecting chamber provided on the casing and in communication withthe liquid separator.

References Cited UNITED STATES PATENTS 2,274,391 2/ 1942 Zwickl 62-5102,277,647 3/1942 Jones 62-5 10 2,888,809 6/1959 Rachfal 62-5l0 FOREIGNPATENTS 76078 10/1954 Netherlands 62510 MEYER PERLIN, Primary Examiner

